Because of excellent properties of polyamide resins, they are expected to be in great demand as engineering plastics. However, some properties of the polyamide resins, such as flexibility, low-temperature impact resistance, resistance to water absorption and resistance to saline solutions, are not always sufficient, and therefore various improvements of these properties have been studied. If the polyamide resins are improved in the flexibility and low-temperature impact resistance, they can be applied to wide uses of from sports goods such as ski boots and sports shoes to industrial parts such as automobile parts, oil tubes, flexible tubes and air hoses, and a great demand therefor can be expected.
For improving the flexibility and the water resistance such as resistance to water absorption or resistance to saline solutions of the polyamide resins, a method of adding ethylene/.alpha.,.beta.-unsaturated monocarboxylic acid copolymer neutralized products (ionomer resins) to the polyamide resins is proposed in Japanese Patent Laid-Open Publications No. 80014/1978, No. 167751/1981, No. 109247/1981 and No. 157451/1981.
However, the polyamide resin compositions proposed in these publications exhibit poor improved effects in the impact resistance such as Izod impact strength, particularly impact resistance at low temperatures, though they can be improved in the water resistance such as resistance to water absorption and resistance to saline solutions.
For improving the impact resistance such as Izod impact strength of the polyamide resins, a method of adding ethylene/.alpha.-olefin copolymer grafted with .alpha.,.beta.-unsaturated carboxylic acids to the polyamide resins is proposed in, for example, Japanese Patent Publications No. 12546/1967 and No. 44108/1980 and Japanese Patent Laid-Open Publication No. 9662/1980.
However, the polyamide resin compositions proposed in these publications show insufficient flexibility and impact resistance at low temperatures. In addition, these polyamide resin compositions have poor moldability depending on the molding process.
As other method to improve the flexibility of the polyamide resins, a method of adding an ethylene/propylene copolymer grafted with .alpha.,.beta.-unsaturated carboxylic acid or an ethylene-1-butene copolymer grafted with said acid to the polyamide resin in the amount exceeding 2/3 of the amount of the polyamide resin and not more than 6 times by weight as much as the polyamide resins is proposed in, for example, Japanese Patent Publication No. 13379/1987. However, the polyamide resin composition proposed in this publication still shows insufficient impact resistance at low temperatures and poor moldability, though the flexibility is satisfactory.
Accordingly, development of a polyamide resin composition having excellent moldability and capable of providing molded products of excellent flexibility, low-temperature impact resistance, resistance to water absorption and resistance to saline solutions has been desired up to now.